The accelerometer on my 920 stopped functioning a while back with no apparent cause. I found forums where others had the same experience, so it happens. I had to exchange mine. I think you'll be in the same boat, but at least you should be under warranty. Good luck.

all accelerometer apps i installed were after the screen stopped rotating....an those were to check the sensors which did not give any readings.

some thing that could be noted is that when i was testing with an accelerometer app...even though no movement was registering....the phone got very hot!!!! of course the heat went away when i closed the app

since im out of the country and wouldnt be back till december, im out of luck on taking it to anywhere...plus even if there was a place here, i dont even have my receipt to show for the warranty!

SOLVED: well not really solved by my screen is back rotating and games and everything is rotating the way it should... how?

i hit it a few times on the back like knocking on a door but nothing worked...may be not hard enough?
i let it drop from 4-5 inches onto my desk (flat on its back) then checked ....and that didnt work.
finally repeated dropping it onto my desk twice in rapid succesion as detailed above and IT WORKED!

I read of others having the same problem and hitting it to get it to work...THE REAL QUESTION IS....DOES IT KEEP WORKING OR DID PROBLEM RETURN?!
i dont know what to expect!

Same problem I met on my TWO Lumia 920 phones(one is replacement). Tried soft reset, hard reset, flashing firms and even a replacement which got the same problem later. All didn't work... THE ONLY OPTIONS YOU SHOULD DO IS TO SLAP THE BACK OF YOUR PHONE HARDLY. It worked for me !!! The tip is after doing this turn on the App Sensor Emitter to check if all the sensors work properly. In my case I found the Accelerometer didn't work on my phone and finally I fixed it by this method